Only college graduates have experienced growth in median weekly earnings since 1979 (in real terms). High school dropouts have, by contrast, seen their real median weekly earnings decline by about 22 percent.
Source:
Bureau of Labor Statistics, Charting the U.S. Labor Market in 2006. See http://www.bls.gov/cps/labor2006/home.htm
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Median weekly earnings of full-time workers (workers 25 years old & older, 2006 dollars)